The McDonnell Douglas DC-9 (initially known as the Douglas DC-9) is a twin-engine, single-aislejet airliner. It was first manufactured in 1965 with its maiden flight later that year. The DC-9 was designed for frequent, short flights. The final DC-9 was delivered in October 1982.

The DC-9-based airliners, MD-80, MD-90 and Boeing 717 later followed in production. With the final deliveries of the 717 in 2006, production of the DC-9/MD-80/90/717 aircraft family ceased after 41 years and over 2,400 units built.

During the 1950s Douglas Aircraft studied a short- to medium-range airliner to complement their higher capacity, long range DC-8. (DC stands for Douglas Commercial.)[1] A medium-range four-engine Model 2067 was studied but it did not receive enough interest from airlines and it was abandoned. In 1960, Douglas signed a two-year contract with Sud Aviation for technical cooperation. Douglas would market and support the Sud Aviation Caravelle and produce a licensed version if airlines ordered large numbers. None were ordered and Douglas returned to its design studies after the cooperation deal expired.[2]

In 1962, design studies were underway. The first version seated 63 passengers and had a gross weight of 69,000 lb (31,300 kg). This design was changed into what would be initial DC-9 variant.[2] Douglas gave approval to produce the DC-9 on April 8, 1963.[2] Unlike the competing but larger Boeing 727trijet, which used as many 707 components as possible, the DC-9 was an all-new design. The DC-9 has two rear-mounted Pratt & Whitney JT8Dturbofan engines, relatively small, efficient wings, and a T-tail.[3] The DC-9's takeoff weight was limited to 80,000 lb (36,300 kg) for a two-person flight crew by Federal Aviation Agency regulations at the time.[2] DC-9 aircraft have five seats across for economy seating. The airplane seats 80 to 135 passengers depending on version and seating arrangement.

The DC-9 was designed for short to medium routes, often to smaller airports with shorter runways and less ground infrastructure than the major airports being served by larger designs like the Boeing 707 and Douglas DC-8. Accessibility and short field characteristics were called for. Turnarounds were simplified by built-in airstairs, including one in the tail, which shortened boarding and deplaning times.

The tail-mounted engine design facilitated a clean wing without engine pods, which had numerous advantages. For example, flaps could be longer, unimpeded by pods on the leading edge and engine blast concerns on the trailing edge. This simplified design improved airflow at low speeds and enabled lower takeoff and approach speeds, thus lowering field length requirements and keeping wing structure light. The second advantage of the tail-mounted engines was the reduction in foreign object damage from ingested debris from runways and aprons. With this position, the engines could ingest ice streaming off the wing roots. Third, the absence of engines in underslung pods allowed a reduction in ground clearance, making the aircraft more accessible to baggage handlers and passengers. Finally, the mounting of the engine to the fuselage reduced the propulsion system's number of potential critical failure points: In a wing-mounted engine configuration, the engine can become detached from the wing or the wing can become detached from the fuselage, whereas the sole concern under a fuselage-mounted configuration is the potential for the engine to become detached from the fuselage.

The problem of deep stalling, revealed by the loss of the BAC One-Eleven prototype in 1963, was overcome through various changes, including the introduction of vortilons, small surfaces beneath the wing's leading edge used to control airflow and increase low speed lift.[4]

The first DC-9, a production model, flew on February 25, 1965.[5] The second DC-9 flew a few weeks later,[3] with a test fleet of five aircraft flying by July. This allowed the initial Series 10 to gain airworthiness certification on November 23, 1965, and to enter service with Delta Air Lines on December 8.[5] The DC-9 was always intended to be available in multiple versions to suit customer requirements,[6] The first stretched version, the Series 30, with a longer fuselage and extended wing tips, flew on August 1, 1966, entering service with Eastern Air Lines in 1967.[5] The initial Series 10 would be followed by the improved -20, -30, and -40 variants. The final DC-9 series was the -50, which first flew in 1974.[3]

The DC-9 was a commercial success with 976 built when production ended in 1982.[3] The DC-9 is one of the longest-lasting aircraft in operation. Its reliability and efficiency led to sales of its successors into the 21st century.[citation needed] The DC-9 family is one of the most successful jet airliners with a total of over 2,400 units produced; it ranks third behind the second-place Airbus A320 family with over 6,000 produced, and the first-place Boeing 737 with over 8,000 produced.

Studies aimed at further improving DC-9 fuel efficiency, by means of retrofitted wingtips of various types, were undertaken by McDonnell Douglas. However, these did not demonstrate significant benefits, especially with existing fleets shrinking. The wing design makes retrofitting difficult.[7]

The final variant was the MD-95, which was renamed the Boeing 717-200 after McDonnell Douglas's merger with Boeing in 1997 and before aircraft deliveries began. The fuselage length and wing are very similar to those of the DC-9-30, but much use was made of lighter, modern materials. Power is supplied by two BMW/Rolls-Royce BR715 high-bypass turbofan engines.

China's Comac ARJ21 is derived from the DC-9 family. The ARJ21 is built with manufacturing tooling from the MD-90 Trunkliner program. As a consequence, it has the same fuselage cross-section, nose profile, and tail.[8]

The original DC-9 (later designated the Series 10) was the smallest DC-9 variant. The -10 was 104.4 ft (31.8 m) long and had a maximum weight of 82,000 lb (37,000 kg). The Series 10 was similar in size and configuration to the BAC One-Eleven and featured a T-tail and rear mounted engines. Power was provided by a pair of 12,500 lbf (56 kN) Pratt & Whitney JT8D-5 or 14,000 lbf (62 kN) JT8D-7 engines. A total of 137 were built. Delta Air Lines was the initial operator.

The Series 10 was produced in two main subvariants, the Series 14 and 15, although, of the first four aircraft, three were built as Series 11s and one as Series 12. These were later converted to Series 14 standard. No Series 13 was produced. A passenger/cargo version of the aircraft with a 136 x 81 in side cargo door forward of the wing and a reinforced cabin floor, was certificated on March 1, 1967. Cargo versions included the Series 15MC (Minimum Change) with folding seats that can be carried at the rear of the aircraft, and the Series 15RC (Rapid Change) with seats removable on pallets. These differences disappeared over the years as new interiors have been installed.[9][10]

The Series 10 was unique in the DC-9 family in not having leading edge slats. The Series 10 was designed to have short takeoff and landing distances without the use of leading edge high-lift devices. Therefore, the wing design of the Series 10 featured airfoils with extremely high maximum lift capability in order to obtain the low stalling speeds necessary for short field performance.[11]

The Series 10 has an overall length of 104.4 feet (31.82 m), a fuselage length of 92.1 feet (28.07 m), a passenger cabin length of 60 feet (18.29 m), and a wingspan of 89.4 feet (27.25 m).

The Series 10 was offered with the 14,000 lbf (62 kN) thrust JT8D-1 and JT8D-7.[9][10]

All versions of the DC-9 are equipped with an AlliedSignal (Garrett) GTCP85 APU, located in the aft fuselage.[9][10]

The Series 14 was originally certificated at an MTOW of 85,700 lb (38,900 kg) but subsequent options offered increases to 86,300 and 90,700 lb (41,100 kg). The aircraft's MLW in all cases is 81,700 lb (37,100 kg). The Series 14 has a fuel capacity of 3,693 US gallons (with the 907 US gal centre section fuel). The Series 15, certificated on January 21, 1966, is physically identical to the Series 14 but has the increased MTOW of 90,700 lb (41,100 kg). Typical range with 50 passengers and baggage is 950 nmi (1,760 km), increasing to 1,278 nmi (2,367 km) at long range cruise. Range with maximum payload is 600 nmi (1,100 km), increasing to 1,450 nmi (2,690 km) with full fuel.[9][10]

The DC-9 Series 10, as with all later versions of the DC-9 is equipped with a two crew analog flightdeck.[9][10]

The aircraft is fitted with a passenger door in the port forward fuselage, and a service door/emergency exit is installed opposite. An airstair installed below the front passenger door was available as an option as was an airstair in the tailcone. This also doubled as an emergency exit. Available with either two or four overwing exits, the DC-9-10 can seat up to a maximum certified exit limit of 109 passengers. Typical all-economy layout is 90 passengers, and 72 passengers in a more typical mixed-class layout with 12 first and 60 economy-class passengers.[9][10]

All versions of the DC-9 are equipped with a tricycle undercarriage, featuring a twin nose unit and twin main units.[9][10]

The Series 20 was designed to satisfy a Scandinavian Airlines request for improved short field performance by using the more powerful engines and improved wings of the -30 combined with the shorter fuselage used in the -10. Ten Series 20 aircraft were produced, all of them Model -21.[12]

The Series 20 has an overall length of 104.4 feet (31.82 m), a fuselage length of 92.1 feet (28.07 m), a passenger cabin length of 60 feet (18.29 m), and a wingspan of 93.3 feet (28.44 m).[9][10]

The DC-9 Series 20 is powered by the 15,000 lbf (67 kN) thrust JT8D-11 engine.[9][10]

The Series 20 was originally certificated at an MTOW of 94,500 lb (42,900 kg) but this was increased to 98,000 lb (44,000 kg), some 8 percent up on the higher weight Series 14s and 15s. The aircraft's MLW is 95,300 lb (43,200 kg) and MZFW is 84,000 lb (38,000 kg). Typical range with maximum payload is 1,000 nmi (1,900 km), increasing to 1,450 nmi (2,690 km) with maximum fuel. The Series 20, using the same wing as the Series 30, 40 and 50, has a slightly lower basic fuel capacity than the Series 10 (3,679 US gallons).[9][10]

The Series 30 was produced to counter Boeing's 737 twinjet; 662 were built, about 60% of the total. The -30 entered service with Eastern Airlines in February 1967 with a 14 ft 9 in (4.50 m) fuselage stretch, wingspan increased by just over 3 ft (0.9 m) and full-span leading edge slats, improving takeoff and landing performance. Maximum takeoff weight was typically 110,000 lb (50,000 kg). Engines for Models -31, -32, -33, and -34 included the P&W JT8D-7 and JT8D-9 rated at 14,500 lbf (64 kN) of thrust, or JT8D-11 with 15,000 lbf (67 kN).

Unlike the -10, the Series 30 had leading edge devices to reduce the landing speeds at higher landing weights; full-span slats reduced approach speeds by 6 knots despite 5000 lbs greater weight. The slats were lighter than slotted Krueger flaps, since the structure associated with the slat is a more efficient torque box than the structure associated with the slotted Krueger. The wing had a six percent increase in chord, all ahead of the front spar, allowing the 15 percent chord slat to be incorporated.[14]

DC-9-31: Produced in passenger version only. The first DC-9 Series 30 flew on August 1, 1966, and the first delivery was to Eastern Airlines on February 27, 1967 after certification on December 19, 1966. Basic MTOW of 98,000 lb (44,000 kg) and subsequently certificated at weights up to 108,000 lb (49,000 kg).

DC-9-32: Introduced in the first year (1967). Certificated March 1, 1967. Basic MTOW of 108,000 lb (49,000 kg) later increased to 110,000 lb (50,000 kg). A number of cargo versions of the Series 32 were also produced:

DC-9-33: Following the Series 31 and 32 came the Series 33 for passenger/cargo or all-cargo use. Certificated on April 15, 1968, the aircraft's MTOW was 114,000 lb (52,000 kg), MLW to 102,000 lb (46,000 kg) and MZFW to 95,500 lb (43,300 kg). JT8D-9 or -11 (15,000 lbf (67 kN) thrust) engines were used. Wing incidence was increased 1.25 degrees to reduce cruise drag.[15] Only 22 were built, as All Freight (AF), Convertible Freight (CF) and Rapid Change (RC) aircraft.

DC-9-34: The last variant was the Series 34, intended for longer range with an MTOW of 121,000 lb (55,000 kg), an MLW of 110,000 lb (50,000 kg) and an MZFW of 98,000 lb (44,000 kg). The DC-9-34CF (Convertible Freighter) was certificated April 20, 1976, while the passenger followed on November 3, 1976. The aircraft has the more powerful JT8D-9s with the -15 and -17 engines as an option. It had the wing incidence change introduced on the DC-9-33. Twelve were built, five as convertible freighters.

The DC-9-30 was offered with a selection of variants of JT8D including the -1, -7, -9, -11, -15. and -17. The most common on the Series 31 is the JT8D-7 (14,000 lbf (62 kN) thrust), although it was also available with the -9 and -17 engines. On the Series 32 the JT8D-9 (14,500 lbf (64 kN) thrust) was standard, with the -11 also offered. The Series 33 was offered with the JT8D-9 or -11 (15,000 lbf (67 kN) thrust) engines and the heavyweight -34 with the JT8D-9, -15 (15,000 lbf (67 kN) thrust) or -17 (16,000 lbf (71 kN) thrust) engines.[9][10]

The DC-9-40 is a further lengthened version. With a 6 ft 6 in (2 m) longer fuselage, accommodation was up to 125 passengers. The -40 was fitted with Pratt & Whitney engines with thrust of 14,500 to 16,000 lbf (64 to 71 kN). A total of 71 were produced. The variant first entered service with Scandinavian Airlines System (SAS) in March 1968.

The Series 50 was the largest version of the DC-9 to enter airline service. It features an 8 ft 2 in (2.49 m) fuselage stretch and seats up to 139 passengers. It started revenue service in August 1975 with Eastern Airlines and included a number of detail improvements, a new cabin interior, and more powerful JT8D-15 or -17 engines in the 16,000 and 16,500 lbf (71 and 73 kN) class. McDonnell Douglas delivered 96, all as Model -51. Some visual cues to distinguish this version from other DC-9 variants include side strakes or fins below the side cockpit windows and thrust reversers rotated about 22 degrees on the original configuration. However various maintenance replacements have seen the thrust reversers in the same position as the -30 and -40.

Delta Air Lines since acquiring Northwest Airlines, has operated a fleet of DC-9 aircraft, most over 30 years old. With severe increases in fuel prices in the summer of 2008, Northwest Airlines began retiring its DC-9s, switching to Airbus A319s that are 27% more fuel efficient.[17][18] As the Northwest/Delta merger progressed, Delta returned several stored DC-9s to service. Delta Air Lines made its last DC-9 commercial flight from Minneapolis/St. Paul to Atlanta on January 6, 2014 with the flight number DL2014.[19][20]

Because of the usage of the aging JT8D engines, as of the late 2000s (decade) DC-9s are considered fuel guzzlers when compared to other more recent airliner designs. Studies aimed at improving DC-9 fuel efficiency, by means of retrofittedwingtip extensions of various types, have not succeeded in demonstrating significant benefits.

With the existing DC-9 fleet shrinking, modifications do not appear to be likely to occur, especially since the wing design makes retrofitting difficult.[7] DC-9s are therefore likely to be further replaced in service by newer airliners such as Boeing 737, Airbus A320, Embraer E-Jets, and the new, emerging Bombardier CSeries.[21] However, it is probable for several DC-9s to continue in service for years.

One ex-SAS DC-9-21 is operated as a skydiving jump platform at Perris Valley Airport in Perris, California. With the steps on the ventral stairs removed, it is the only airline transport class jet certified to date by the FAA for skydiving operations as of 2008.[22]

On March 16, 1969, Viasa Flight 742, a DC-9-32, crashed into the La Trinidad neighborhood of Maracaibo during a failed take-off. All 84 people on board the aircraft, as well as 71 people on the ground, were killed. With 155 dead in all, this was the deadliest crash involving a member of the original DC-9 family, as well as the worst crash in aviation history at the time it took place.[28]

On June 6, 1971, Hughes Airwest Flight 706, midair collision between commercial DC-9 and a U.S. Marine Corp jet. All 49 people on board the DC-9 died; one of two pilots from the F-4E Phantom ejected and survived.

On January 21, 1972, a Turkish Airlines DC-9-32 TC-JAC diverted to Adana, Turkey after pressurization problems. The aircraft hit the ground during downwind on the 2nd approach and caught fire. There was only one fatality.[citation needed]

On January 26, 1972, JAT Flight 367 from Copenhagen to Belgrade, DC-9-32 registration YU-AHT, was destroyed in flight by a bomb placed on board. The sole survivor was a flight attendant, Vesna Vulović, who holds the record for the world's longest fall without a parachute when she fell some 33,000 ft (10,000 m) inside the tail section of the airplane and survived.

On November 10–11, 1972, Southern Airways Flight 49 was hijacked while departing Birmingham, Alabama's airport by three armed men. The hijackers then proceeded to fly the passengers and crew to multiple locations in the United States, Canada, and Cuba, including Chattanooga, Tennessee, where the less-than-demanded ransom money was delivered, the now-defunct McCoy Air Force Base in Orlando, Florida, where the FBI shot out two of the DC-9's four main landing wheels, and Havana, where the 30 hours and 4,000 miles (6,400 km) odyssey came to an end with no fatalities or injuries between the passengers and crew members. This incident is notable for being the first hijacking in which an aircraft left Cuba with the hijackers on board.[35]

On April 4, 1977, Southern Airways Flight 242, a DC-9-31, lost engine power in a storm then crash landed onto a highway in New Hope, Georgia, US, striking road side buildings. The crash and fire resulted in the death of both flight crew and 61 passengers. Nine people on the ground also died. Both flight attendants and 20 passengers survived.[38][39]

On June 26, 1978, Air Canada Flight 189, a DC-9 overran the runway in Toronto after a blown tire aborted the takeoff. Two of the 107 passengers and crew were killed.[40]

Itavia DC-9 (I-TIGI) was destroyed in an accident at Ustica. Shown in the "Museo della Memoria" opened in Bologna in 2007.

On June 27, 1980, Aerolinee Itavia Flight 870, a DC-9-15 suffered an in-flight explosion and crashed into the sea near the Italian island of Ustica. All 81 passeners and crew on board were killed. Italian prosecutors and the Parliament Commissions came to the conclusion that the DC-9 was mistakenly identified by French, US and Italian fighters as an executive jet believed to be carrying Libyan leader M. Qaddafi and shot down.[42][43][44]

On December 7, 1983, the Madrid Runway Disaster took place where a departing IberiaBoeing 727 struck an Aviaco Douglas DC-9 causing the death of 93 passengers and crew. All 42 passengers and crew on board the DC-9 were killed.

On June 21, 1993, Garuda Indonesia Flight 630, a DC-9-32 PK-GNT landed heavily on runway 09 (forces of 5g) and taxied safely to apron at Ngurah Rai International Airport in Denpasar, Bali, Indonesia. Major structural damage was discovered there. The aircraft was high on approach, which was overcorrected, causing the aircraft coming too low. Thrust was increased and the DC-9 then struck the runway in a nose up attitude. No deaths.

On July 2, 1994, USAir Flight 1016, a DC-9-31 N954VJ crashed in Charlotte, North Carolina while performing a go-around because of heavy storms and wind shear at the approach of runway 18R. There were 37 fatalities and 15 injured among the passengers and crew. Although the airplane came to rest in a residential area with the tail section striking a house, there were no fatalities or injuries on the ground.

On May 11, 1996, ValuJet Flight 592, a DC-9-32 N904VJ crashed in the Florida Everglades due to a fire caused by the activation of chemical oxygen generators illegally stored in the hold. The fire damaged the plane's electrical system and eventually overcame the crew, resulting in the deaths of 110 people.

On October 6, 2000, Aeroméxico Flight 250, a DC-9-31 en route from Mexico City to Reynosa, Mexico, could not stop at the end the of runway and crashed into houses and fell into a small canal. Four people on the ground were killed. None of 83 passengers and 5 crew members were killed. The DC-9 was heavily damaged and classified as a loss. The runway had seen heavy rainfall as a result of Hurricane Keith.[51]

^Priest, Lisa; Rick Cash (2005-03-08). "Takeoffs and landings always pose risk of calamity, as history shows" (Fee required.). Globe & Mail (Toronto, Ontario, Canada). Retrieved 2008-11-23. The last time an aircraft skidded off the runway in Toronto, seriously injuring passengers, was more than a quarter-century ago. On June 26, 1978, an Air Canada DC-9 skidded off a taxi strip at Toronto International Airport (what is today Pearson International Airport) during an aborted takeoff, then belly-flopped into a swampy ravine, killing two passengers and injuring more than a hundred others.[dead link]